The overall objective of the proposed research is to clarify the mechanics of the papillary muscle and to organize an analysis of the intact left ventricle. The proposed research aims to complete a program of experiments on the stimulated and unstimulated cat and rabbit papillay muscles, to obtain information leading to mathematical description of its behavior (constitutive equation). This generalized model for heart muslce is essential before organizing a three-dimensional analysis of the intact venticle. Pressure-volume relationship of the intact ventricle will be derived analytically and compared with experimental results of other investigators in the field. We have developed a new, computer interfaced muscle testing facility for experiments on the papillary muscle. During the course of development of the testing device experiments on the passive muscle and the stimulated muscle were also done and results published. To achieve our objective, we plan to continue the exeriments, follow small amplitude, high frequency vibration procedures on the muscle during the twitch, during tetanized state, and in the passive state. Classical quick stretch, quick release procedure will also utilized. Because of special features afforded by out testing apparatus (performance alterability) we also plan to follow procedures of other investigators and repeat their experiments. Data from different experiments. Data from different experiments will be scrutinized to resolve conflicts.